Because it's there …

… Bryan Appleyard — Philae: A Brave, Drifting Thing. (Hat tip, Dave Lull.)

Up to the landing it all worked perfectly, making this, without doubt, the most astounding feat of navigation of the space era. In fact, it probably outshines all the voyages of the greatest earthbound navigators — Ferdinand Magellan, Christopher Columbus and Vasco da Gama. Branson said “space is hard” of a mission that involved nothing more than getting a rocket with a few people on board 60 miles off the Earth’s surface; by that standard Rosetta was impossible, cosmically so.